1. Field of the Invention
The present invention relates to a multi-antenna and a radio apparatus including thereof (e.g., a portable radio apparatus, such as a mobile phone).
2. Description of the Related Art
In recent years, wireless technology has been spread which is for a multi-antenna including multiple antennas, such as a diversity antenna and MIMO; and a technique has been demanded that is for enhancing isolation of multi-antennas. Furthermore, for an antenna to be installed in a radio apparatus, such as a mobile phone and a mobile device, downsizing has been demanded in accordance with downsizing of mobile devices.
As a technique for enhancing isolation, a method has been reported in Non-Patent Document 1 such that, compared to FIG. 12A of related art, by newly locating a parasitic element C between antenna elements (dipoles) A and B, as illustrated in FIG. 12B, additional coupling paths are created so as to generate a cancellation electric current.
Additionally, as another technique for enhancing isolation, an antenna has been proposed in Patent Document 1 that includes antenna units 120 and 130; a coupling conductor line 140; and, further, a ground conductive line 150, as illustrated in FIG. 13. Here, a method has been reported such that, by providing the coupling conductor line 140 and the ground conductive line 150, interference between resonance modes excited by the antenna units 120 and 130 is reduced.
Alternatively, as a technique for enhancing isolation while reducing reduction of a space, an antenna has been proposed in Patent Document 2 that is adapted for multiple frequencies by causing feed elements 510 and 520, and a parasitic element 530 to be coupled in a contactless manner, as illustrated in FIG. 14. Specifically, a method has been reported in Patent Document 2 that is for causing capacitive coupling to a parasitic element.